Computer simulations of the copolymerization of styrene and methyl methacrylate have been carried out in an attempt to assess the relative importance of the cross and the two homotermination processes. During the copolymerization, termination by methacrylyl-methacrylyl interaction is of relatively little significance. Termination occurs mainly through styryl-styryl and styryl-methacrylyl interaction. Features of models commonly used to describe polymerization kinetics are discussed.